Wireless LAN system and a transmitter-receiver in a wireless LAN system

ABSTRACT

In a wireless LAN system chiefly using a millimeter wave, a satellite station is provided with an active phased planar-array antenna, the radiating directivity characteristic of which can be freely changed. When a master station receives a control frame transmitted from the satellite station prior to the commencement of normal communication, the master station transmits a carrier wave. The satellite station determines such a directivity characteristic of an antenna as to receive this carrier wave with the strongest intensity, and fixes the characteristic. Thus, an optimal communication environment can be secured. When the number of errors in a received data frame or the receiving electric field intensity received by the satellite station in normal communication is inferior to a respective predetermined threshold, the deterioration of the communication environment can be coped with by determining again. The power consumption of the master station can be reduced by making the transmitting power of a carrier wave for determining less than the transmitting power at the time of normal communication.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of application Ser. No. 09/040,426,filed Mar. 18, 1998, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a local area network (LAN), morespecifically to the optimization of communication quality for realizingan optimal communication environment between a wireless LAN satellitestation and a master station in a wireless LAN system mainly using anelectromagnetic wave in a millimeter wave range.

2. Description of the Related Art

These days a LAN has become popular and the amount of data handled on aLAN has been also increasing. On the other hand, data terminalsincluding a personal computer have been improved in communicatingfunctions, and have been miniaturized. Under these circumstances, theneed for data communication in a mobile environment is advocated, andattention is being paid to a wireless LAN system.

So far an electromagnetic wave in an ISM range, that is, approximatelythe 1 to 3 GHz range, has been used for a wireless LAN system. However,since this bandwidth is also used for industrial purposes or electronicovens, a large amount of noise is generated. To suppress this largeamount of noise it is necessary to employ a spread spectrumcommunication method, which has made a system complicated. The systemalso has a drawback that in this wave range a bandwidth required for ahigh speed transmission cannot be secured.

For this reason, attention is currently being paid to a millimeter waverange of 50 to 70 GHz which is still an unused wave range for datacommunication.

An electromagnetic wave in this wave range is characterized in that itis strong to keep straight on, and it is easily absorbed by oxygen andglass. For example, since there is little possibility that anelectromagnetic wave leaks outside when it is used in an officeenvironment, it is effective in security. Furthermore, since it is anunused band width, and thereby there is no need to employ a spreadspectrum communication method, the system can be simplified, comparedwith the case when an ISM range is used. Since in a millimeter waverange a band with required for a high speed transmission can be secured,it is a very promising wave range at present when a high speedtransmission of over 100 Mbps is becoming popular in a wired LAN system.

However, the wireless LAN system using an electromagnetic wave in amillimeter range has the following problems.

The first problem is that a communication environment rapidlydeteriorates due to a subtle change of the position and direction of anantenna of a satellite station. In order to expand acommunication-available area in a millimeter wave wireless LAN system anantenna with a rather broad radiating directivity is usually used forthe master station. However, a millimeter wave is strong to keepstraight on and is easily absorbed by oxygen. There is also influencefrom interference among satellite stations and multipath interferencewhich is caused by being a plurality of routes for an electromagneticwave transmitted from a satellite station. For this reason, to secure afavorable communication environment, it is necessary to sharpen theradiation characteristic of the antennae of satellite stations and toalways direct the radiation characteristic of the satellite stationsexactly to the antenna of the master station.

To avoid the influence from interference among satellite stations andmultipath, the use of diversity antennae and the introduction of aspread spectrum communication method can be considered. However, it istechnically difficult to implement these methods in a millimeter waverange, and even if it can be implemented, the system becomescomplicated. This is the second problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a millimeter wavewireless LAN system in which a favorable communication environment canbe secured between a satellite station and a master station by directingthe radiation characteristic of an antenna of a wireless LAN satellitestation exactly to an antenna of the master station in view of the abovementioned problems.

To attain the object of the present invention as described above, awireless LAN system of the present invention comprises a wireless LANmaster station for supporting communication between satellite stationsbelonging to the master station and one or more wireless LAN satellitestations. A transmitter-receiver in the system being a satellite stationof the LAN system comprises an antenna, the directivity characteristicof which can be dynamically changed when receiving waves from the masterstation, control frame transmitting means for transmitting a controlframe to the master station prior to the commencement of communication,and antenna directivity characteristic controlling means for determiningsuch a directivity characteristic that the receiving electric fieldintensity of a carrier wave transmitted from the master station when thecontrol frame is transmitted may become a maximum by changing thedirectivity characteristic of an antenna. A transmitter-receiver forcommunicating with another party in the system being the master stationcomprises carrier wave transmitting means for transmitting a carrierwave when receiving the control frame. In the wireless LAN system of thepresent invention, prior to the commencement of communication, asatellite station transmits a control frame to the master station. Whenthe master station receives the control frame from the satellitestation, it starts to transmit a carrier wave. When the satellitestation receives the carrier wave transmitted from the master station,it changes the directivity characteristic of an antenna, and determinessuch a directivity characteristic that the receiving electric fieldintensity of the carrier wave may become a maximum.

After that, by using the directivity characteristic obtained from theresult of the determination, communication between a satellite stationand the master station can be carried out in an optimal communicationenvironment.

For an antenna of a satellite station an active phased planar-arrayantenna can be used. Thus, without adjusting the physical position of anantenna of a satellite station, communication between a satellitestation and the master station can be carried out in an optimalcommunication environment.

Further, after the satellite station starts to exchange data frames ascommunications with the master station, conditions can be set for thenumber of errors detected in a data frame that are allowed to bereceived, or the electric field intensity of the data frame that isallowed to be received, and when the conditions are not met, an optimalantenna directivity characteristic can be determined again. Thus, thedeterioration of communication quality occurring because a satellitestation or the master station moves or because the position of anantenna is shifted due to some cause, can be automatically coped with,and an optimal communication environment can be always provided.

Furthermore, the transmitting power of a carrier wave which istransmitted when the master station receives a control frame from asatellite station, can be less than the transmitting power at the timeof the transmission of a data frame as normal communication. Thus, thepower consumption of the master station can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the following detaileddescription, when taken in conjunction with the accompanying drawings,in which:

FIG. 1 is a block diagram showing the theoretical configuration of thepresent invention.

FIG. 2 shows the basic configuration of a wireless LAN system of thepresent invention.

FIG. 3 shows an active phased planar-array antenna as an example of anantenna for a satellite station.

FIG. 4 shows the change of radiating directivity characteristic of anactive phased planar-array antenna.

FIG. 5 is a block diagram showing the configuration of a wireless LANsatellite station.

FIG. 6 is a flowchart of an optimizing process of basic communicationquality executed by the control unit shown in FIG. 5.

FIG. 7 shows the configuration of the determining function control unitshown in FIG. 5.

FIG. 8 shows the configuration of an antenna directivity characteristiccontrol unit.

FIG. 9 shows a method for determining an antenna radiation directivitycharacteristic of a satellite station.

FIG. 10 shows a method for sending a control frame to the master stationprior to the determination of an antenna radiation directivitycharacteristic.

FIG. 11 shows the configuration of the receiving control unit shown inFIG. 5.

FIG. 12 shows the configuration of an electric field densitydetecting/storing unit.

FIG. 13 shows the configuration of a control frame generating unit.

FIG. 14 shows the configuration of the power feeding power control unitshown in FIG. 5.

FIG. 15 shows the configuration of a transmitting control unit.

FIG. 16 shows the configuration of an FCS error frame detectingunit/counter.

FIG. 17 is a block diagram showing the configuration of a wireless LANmaster station.

FIG. 18 is a basic flowchart of processes executed by the control unitshown in FIG. 17.

FIG. 19 shows the configuration of the determining function control unitshown in FIG. 17.

FIG. 20 shows the configuration of a frame distinguishing unit.

FIG. 21 shows the configuration of the power feeding power control unitshown in FIG. 17.

FIG. 22 shows an example of a format for a control frame.

FIG. 23A shows a case where the difference between the maximum value andthe minimum value of electric field intensity is regarded as a successas a result of determination.

FIG. 23B shows a case where the difference between the maximum value andthe minimum value of electric field intensity is regarded as a failureas a result of determination.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of the principle and the configuration of thepresent invention. This is a block diagram of the theoreticalconfiguration of a wireless LAN system connected to a backbone LAN andcomprises a wireless master station supporting communication betweensatellite stations belonging to the master station and one or morewireless LAN satellite stations. The master station and satellitestations are transmitter-receivers which can communicate with eachother.

As shown in FIG. 1, a satellite station 4 comprises an antenna unit 1, acontrol frame transmitting unit 2 and an antenna directivitycharacteristic control unit, whereas the master station 6 comprises acarrier wave transmitting unit 5.

When the antenna unit 1 receives electric waves from the master station,the antenna unit 1 can change the directivity characteristic of theantenna unit 1. Prior to the commencement of communication with themaster station or another satellite station or when communicationconditions deteriorate after the commencement of communication, thecontrol frame transmitting unit 2 transmits a control frame to themaster station 6.

The antenna directivity characteristic control unit 3 changes thedirectivity characteristic of the antenna unit 1, for example, an activephased planar-array antenna, and determines such a directivitycharacteristic that the receiving electric field density of a carrierwave transmitted from the master station when the master stationreceives the control frame may become a maximum.

The carrier wave transmitting unit 5 starts to transmit a carrier wavewhen the master station receives the control frame from a satellitestation.

Usually LAN data has a characteristic of being concentrated andcommunicated at a certain time like a data burst, and generallyspeaking, when there is no data to be communicated, a carrier wave isnot transmitted from the master station of the LAN system, still less adata frame. For this reason, in the present invention, a control frameis transmitted from the control frame transmitting unit 2 of a satellitestation to the master station. In the master station 6, when the masterstation receives the control frame, the master station starts totransmit only a carrier wave from the carrier wave transmitting unit 5.In the satellite station 4, while this carrier wave is beingtransmitted, such a directivity characteristic of antenna unit 1 thatthe receiving electric field intensity of the carrier wave becomes amaximum, is determined by the antenna directivity characteristic controlunit 3.

In the present invention, when the antenna unit 1 is composed of anactive phased planar-array antenna, the directivity characteristic ofthe antenna unit 1 of the satellite station can also be made broad bytransmitting the control frame using only one element out of a pluralityof elements in the array of an active phased planar-array antenna, whenthe satellite station is transmitting the control frame using thecontrol frame transmitting unit 2. Further, in this case, by increasingthe power feeding power for one element used for transmitting thecontrol frame, the radiating power of the control frame can never beless than the radiating power in the case where all elements are used,and the control frame can be transmitted to the master station withoutfail.

Furthermore, in the present invention, after such a directivitycharacteristic that the receiving electric field intensity in thesatellite station of a carrier wave transmitted from the master stationmay become a maximum, is determined, and the directivity characteristicof the antenna unity 1 is fixed to that direction, a data frame isstarted to be transmitted and received between the master station andthe satellite station. After that an antenna directivity characteristicis determined again, if necessary.

For example, when an error is detected in the data frame received fromthe master station, such as a frame check sequence error, or the numberof the detected error frames exceeds a predetermined number, by thecontrol frame transmitting unit 2 transmitting the control frame, by thecarrier wave transmitting unit 5 starting to transmit a carrier wave andthe antenna directivity characteristic control unit 3 determining adirectivity characteristic, the communication quality of a wireless LANcan be optimized again.

FIG. 2 shows the basic configuration of a wireless LAN system of thepresent invention. For example, in FIG. 2 a wireless LAN systemcomprises a wireless LAN master station 12 connected to a wired backboneLAN 11, and a plurality of wireless LAN satellite stations 15 connectedto data terminals 14 respectively. The antenna of the wireless LANmaster station 12 has a broad radiating directivity characteristic 13,whereas the satellite station antennae 16 of the wireless LAN satellitestations 15 have an acute radiating directivity characteristic 17.

Since, general speaking, data is often transmitted like a burst in a LANsystem, the wireless LAN master station 12 does not transmit a carrierwave when there is no data to be transmitted. Therefore, in thisembodiment, when the satellite station 15 starts to operate, a connecteddata terminal 14 such as a personal computer starts to operate or thedata 5 terminal 14 starts to communicate, the satellite station 15transmits a control frame different from a normal LAN data frame to themaster station 12, the master station receives the control frame andstarts to transmit only a carrier wave. The antenna 16 of the satellitestation 15 is provided by an active phased planar-array antenna. Thesatellite station 15 determines such a direction where a carrier wavetransmitted from the master station can be received with the maximumintensity, and good communication quality can be secured by conformingthe direction of a radiating beam of an antenna, that is, the radiatingdirectivity characteristic, to the determined direction.

In FIG. 2, equipment in various forms such as PC card type, terminalbuilt-in type, set top type, etc., is used for wireless LAN site station15. There are also an antenna 16 incorporated satellite station, and asatellite station 15 with an antenna 16 connected by a signal wire.There is no restriction in the configuration and form of a satellitestation 15 and an antenna 16.

Furthermore, as for the antenna 16 one antenna can be used for bothtransmission and reception, or different antennae can be used fortransmission and reception. In this embodiment it is assumed thatdifferent antennae are used for transmission and reception, anddifferent frequencies are used for transmission and reception.

FIG. 3 shows an active phased planar-array antenna as an example of anantenna for a satellite station 16 shown in FIG. 2. In the drawing, anactive phased planar-array antenna 21 is composed of a plurality, 9 inthis embodiment, of patch elements 22. A x phase shifter 23 and a yphase shifter 24 are provided corresponding to each patch element 22.The x phase shifter 23 changes a power feeding phase to a side parallelto the y axis of a patch element in order to change the directivitycharacteristic on a x-z plane, and the y phase shifter 24 changes apower feeding phase to a side parallel to the x axis. To each x phaseshifter 23 and each y phase shifter 24 are connected an excitationcontroller 25 of the x phase shifter and an excitation controller 26 ofthe y phase shifter, respectively.

Although an antenna array of an active phased planar-array antenna 21 iscomposed of 9 patch elements shown in FIG. 3, the number of elements isnot limited to this. Furthermore, although the shape of an element is asquare, the shape of the element can be any form, such as a form inwhich one pair of the opposite angles of a square is cut, a circle,di-pole type, etc.

FIG. 4 shows the change of the radiating directivity characteristic ofan active phased planar array antenna in the case where the antenna isseen from the y direction. In the drawing it is seen that the directionof the radiating directivity characteristic of the entire antennachanges on a x-z plane by controlling the x phase shifter 23corresponding to each patch element 22.

FIG. 5 is a block diagram of the configuration of a satellite station.In the drawing a satellite station 31 is connected with a receivingantenna 32 and a transmitting antenna 33. The satellite station roughlycomprises a radio unit 34, a control unit 35, a LAN function unit 36 anda timer 37.

The radio unit 34 is connected with the receiving antenna 32 and atransmitting antenna 33, and comprises a modulator/demodulator, a phaseshifter, a phase shifter controller, an antenna power feeding circuit, aburst switch circuit, etc.

The LAN function unit 36 comprises a data transmitting and receivingcontrol function, a carrier detecting function, an FCS (frame checksequence) error detecting function, a collision detecting function, apreamble adding function, a terminal interface, etc.

The control unit 35 comprises a determining function control unit 41, anantenna directivity characteristic control unit 42, a receiving controlunit 43, an electric field intensity detecting/storing unit 44, acontrol frame generating unit 45, a power feeding power control unit 46,a transmitting control unit 47 and an FCS error frame detectingunit/counter 48.

FIG. 6 is a flowchart of the optimizing process of basic communicationquality executed by a control unit 35 shown in FIG. 5.

First, in step S101, an antenna directivity characteristic control unit42 receives an instruction to start to determine from the detectingfunction control unit 41, and instructs the radio unit 34 to use onlyone patch element out of a plurality of patch elements composing anactive phased planar-array antenna being the transmitting antenna 33 tobroaden the radiating directivity characteristic of the transmittingantenna 33.

In step S102 the transmitting control unit 47 outputs a control framegenerated by the control frame generating unit 45 to the radio unit 34to make the radio unit 34 transmit the control frame.

In step S103 the receiving control unit 43 makes the radio unit 34receive a carrier wave transmitted from the master station when themaster station receives the control frame, and the antenna directivitycharacteristic control unit 42 determines such a directivitycharacteristic that a carrier wave with the maximum intensity may bereceived while changing the directivity characteristic of the receivingantenna 32.

In step S104 the electric field intensity detecting storing unit 44stores such a directivity characteristic of the receiving antenna thatthe receiving electric field intensity may become a maximum.

In step S105 the antenna directivity characteristic control unit 42instructs the radio unit 34 so that the receiving antenna 32 and thetransmitting antenna 33 may have such a directivity that the receivingelectric field intensity stored in the electric field intensitydetecting storing unit 44 may become a maximum, and terminates theoptimizing process. The configuration of the control unit 35 isdescribed in detail below.

FIG. 7 shows the configuration of the determining function control unitshown in FIG. 5.

In the drawing, the determining function control unit 41 comprises thedetermined state storing/instructing unit 51. For example, when an erroris detected upon receiving a control frame returned from the masterstation, when the electric field intensity of a carrier wave receivedfrom the master station is detected and found not to meet therequirements described later by the electric field intensitydetecting/storing unit 44, when errors are frequently detected in normaldata frames by the FCS error frame detecting unit/counter 48, and when adata terminal start signal is input, the determined statestoring/instructing unit 51 sends a signal for instructing to start todetermine to the control frame generating unit 45, etc.

FIG. 8 shows the configuration of an antenna directivity characteristiccontrol unit. In the drawing, the antenna directivity characteristiccontrol unit 42 comprises a directivity 20 instructing unit 52 and ausing element instructing unit 53.

The control by the antenna directivity characteristic control unit isfurther described below. As mentioned before, in a LAN satellitestation, an active phased planar-array antenna the radiating directivitycharacteristic of which can be freely changed consecutively is used forreception. As explained in FIG. 4, the direction of the radiatingdirectivity characteristic can be freely changed on a x-z plane bychanging a power feeding phase for a patch element 22 using a phaseshifter corresponding to each patch element 22. The same applies to ax-y plane. Therefore, the direction of the radiating directivitycharacteristic can be freely changed on a hemispherical plane of anantenna plane by changing each power feeding phase using a x phaseshifter 23 and a y phase shifter 24.

The active phased planar-array antenna is further described below. Thisantenna is an antenna on a dielectric base plate on which a plurality ofantenna elements, that is, patch elements, are two dimensionally (on aplane) arrayed. Each patch element is provided with a phase shifter, andthe radiating direction of electromagnetic waves, that is radiatingdirectivity characteristic, can be actively changed without changing thephysical direction of an antenna by changing the phase of excitation ofa respective patch elements consecutively using the phase shifters. Thisantenna is, for example, used for radar, etc. An antenna with an acuteradiating directivity characteristic is also configured by arraying manypatch elements. On the contrary, abroad radiating directivitycharacteristic having a half power angle of 90 to 120 degrees or morecan also be realized.

FIG. 9 shows a method for determining an antenna radiation directivitycharacteristic of a satellite station, that is, a method of determiningthe direction of the master station. As explained in FIG. 3, on thesatellite station receiving antenna 32, nine patch elements aretwo-dimensionally arrayed, the satellite station receiving antenna 32has an acute radiating directivity characteristic, and the satellitestation receiving antenna determines so that the radiating directivitycharacteristic may be directed to the master station (54).

First, angle θ is decided by shifting the radiating directivitycharacteristic on an x-y plane, that is, determining horizontally (55).Then, angle φ is decided by determining on a z-a plane (56). Thus, theradiating directivity characteristic of the satellite station antenna 57is directed to the master station (54). FIG. 10 shows a method forsending a control frame to the master station prior to the determinationof an antenna radiation directivity characteristic.

In the drawing, a control frame is sent to the master station using outof a plurality of patch elements composing the satellite stationtransmitting antenna 33, for example, only a patch element at the center58. In this case, the radiating directivity characteristic of thesatellite station 59 is made broad by using only one patch element, andthe control frame 60 is transmitted in a broad direction. Thus, inwhichever direction the master station is located, the master canreceive the control frame.

The directivity instructing unit 52 shown in FIG. 8 stores the values ofθ and φ being the result of the determination of an antenna directivitycharacteristic, reports the values to the radio unit 34, and fixes theradiating directivity characteristic of both the transmitting antenna 33and the receiving antenna 32. That is, at the time of normal datacommunication, both antenna for transmission and reception are directedto the direction decided by the optimal values of a θ and φ. When theusing element instructing unit 53 receives a determination startinstructing signal from the determining function control unit 41, theusing element instructing unit 53 reports to the radio unit 34 aninstruction to transmit a control frame using only one element of thetransmitting antenna 33.

FIG. 11 shows the configuration of the receiving control unit shown inFIG. 5. In the drawing, the receiving control unit 43 comprises acontrol frame FCS error checking unit 64, a data switch unit 65 and arandom back-off timer 66.

When the control frame FCS error checking unit 64 receives a data inputfrom the radio unit 34 and detects an error in a control frame returnedfrom the master station, the control frame FCS error checking unit 64judges that a collision occurs with a normal data frame sent fromanother satellite station, and instructs the determining functioncontrol unit 41 to determine again after a random back-off time. At thetime of the determination of an antenna direction and at the time ofnormal data frame communication, the data switch unit 65 performs aswitch function to output a control frame as data to the electric fieldintensity detecting/storing unit 44, and to output data to both the LANfunction unit 36 and the electric field intensity detecting/storing unit44, respectively. The random back-off timer 66 is a timer for deciding arandom back-off time for transmission until transmitting a control frameagain after detecting a collision.

FIG. 12 shows the configuration of an electric field densitydetecting/storing unit. In the drawing, the electric field intensitydetecting/storing unit 44 comprises an electric field intensitydetecting unit 68 and a storing unit 69.

When the electric field intensity detecting unit 68 determines anantenna direction, the electric field intensity detecting unit 68detects the electric field intensity of a carrier wave transmitted fromthe master station, and reports to the storing unit 69 the angle of theradiating directivity characteristic at that time. When the detectedelectric field intensity is less than the predetermined threshold evenif the angle of the radiating directivity characteristic is changed, theelectric field intensity detecting unit 68 instructs the determiningfunction control unit 41 to determine again.

At the time of normal data communication the electric field intensitydetecting unit 68 monitors the receiving electric field intensity of anormal data frame, and when the value is less than the predeterminedthreshold, the electric field intensity detecting unit 68 instructs thedetermining function control unit 41 to determine the directivitycharacteristic of the antenna again in the same way.

The storing unit 69 receives an output from the electric field intensitydetecting unit 68, stores the values of θ and φ when the maximumdetected receiving strength is more than the predetermined minimumvalue, that is, a threshold, reports the values to the antennadirectivity characteristic control unit 42, and fixes the antennadirectivity characteristic to the direction of the θ and φ.

FIG. 13 shows the configuration of a control frame generating unit 45.In the drawing a control frame memory ROM 71 receives an instruction tostart to determine from the determining function control unit 41, andoutputs the control frame stored in the ROM to the transmitting controlunit 47.

FIG. 14 shows the configuration of a power feeding power control unit46. In the drawing a power reinforcement instructing unit 72 receives aninstruction to start to determine from the determining function controlunit 41, sends an instruction to increase feeding power to only anantenna used for transmitting a control frame, that is, one patchelement, to the radio unit 34, and instructs to restore the feedingpower to normal after transmitting the control frame. As explained inFIG. 10, this is because when transmitting a control frame, only onepatch element is used in order to broaden the radiating directivitycharacteristic, the radiating power of an antenna becomes small, andtherefore the feeding power for the patch element is increased.

FIG. 15 shows the configuration of a transmitting control unit 47. Inthe drawing, a data switch unit 73 performs a switch function, that is,when a satellite station determines an antenna directivitycharacteristic according to an instruction from the determining functioncontrol unit, the data switching unit 73 sends a control frame inputfrom the control frame generating unit 45 to the radio unit 34, and atthe time of normal data communication executes a switching function tosend a normal data frame from the LAN function unit 36 to the radio unit34.

FIG. 16 shows the configuration of an FCS error frame detectingunit/counter 48. In the drawing an FCS error counter/storing unit 74receives an input from the LAN function unit 36, at the time of normaldata communication counts the number of data frames in which an error isdetected by the LAN function unit 36, and for example, when receives insuccession a predetermined number of error frames, the FCS error framedetecting unit/counter 48 instructs the determining function controlunit 41 to start determining.

Further, when an error frame is first received, the FCS errorcounting/storing unit 74 issues an instruction to start to the timer 37,and when it receives the number of error frames predetermined before thetime-out, instructs to start to determine to the determining functioncontrol unit 41. This operation is further described later.

FIG. 17 is a block diagram showing the configuration of a wireless LANmaster station. In the drawing, a receiving antenna 82 and atransmitting antenna 83 are connected to the master station 81. Themaster station roughly comprises a radio unit 84, a control unit 85 anda LAN function unit 86.

The radio unit 84 comprises a modulator/demodulator, a phase shifter, aphase shifter controller, an antenna power feeding circuit, a burstswitch circuit, etc. The control unit 85 comprises a determiningfunction control unit 87, a frame distinguishing unit 88 and a powerfeeding power control unit 89. Furthermore, the LAN function unit 86comprises a data transmitting/receiving control function, a carrier wavedetecting function, a collision detecting function, a preamble addingfunction, a data returning function and a backbone interface, etc.

FIG. 18 is a basic flowchart of processes executed by the control unit85 shown in FIG. 17.

First, in step S111 the radio unit 84 receives a frame transmitted by asatellite station 31, and the frame is input to the frame distinguishingunit 88.

In step S112 the frame distinguishing unit 88 judges whether or not areceived frame is a control frame, and if so, the flow proceeds to stepS113. If the received frame is not a control frame, the flow proceeds tostep S114, and the frame is output to the LAN function unit 86 to makethe LAN function unit transfer the frame to a backbone LAN, and then theflow returns to step S111.

In step S113 the determining function control unit 87 instructs theradio unit 84 to transmit a carrier wave from the transmitting antenna83 while a satellite station is determining the directivitycharacteristic of an antenna, and then the flow returns to step S11. Atthis time, the power feeding power control unit 89 controls the feedingpower of the radio unit 84 so that the satellite station may obtain anelectric field intensity sufficient to determine the directivitycharacteristic of the antenna.

Each of units composing the control unit 85 is further described indetail below.

FIG. 19 shows the configuration of the determining function control unit87 shown in FIG. 17. In the drawing, when the determining functioncontrol unit 87 is reported to receive a control frame from the framedistinguishing unit 88, the determining function control unit 87instructs the radio unit 84 to transmit a carrier wave. If at this timethe saving of the power is required, the determining function controlunit 87 instructs the power feeding power control unit 89 to reduce thetransmitting power of the carrier wave.

FIG. 20 shows the configuration of the frame distinguishing unit 88. Inthe drawing the control frame distinguishing unit 91 judges whether ornot when receiving an input of a receiving frame from the radio unit 84,the frame is a control frame, and outputs the result of the judgement tothe switch unit 92. If the frame is a control frame, the switch unit 92reports to the determining function control unit 87 that the switch unit92 has received a control frame. On the contrary, if the frame is not acontrol frame, the switch unit 92 sends the received frame to the LANfunction unit 86.

FIG. 21 shows the configuration of a power feeding power control unit89. In the drawing, a power regulating unit 93, when a carrier wave isbeing sent, reduces feeding power according to an instruction from thedetermining function control unit 87, and feeds the reduced power to theradio unit 84.

Although so far the configuration of a LAN satellite station and themaster station are mainly described, the optimization of communicationquality of this embodiment is further described in detail below.

In FIG. 5, as described above, in a LAN satellite station 31, first, forexample, when a satellite station starts to operate, an instruction totransmit a control frame is issued from the determining function controlunit 41 to the control frame generating unit 45, and a control framedifferent from a normal LAN data frame is transmitted to the masterstation via the transmitting control unit 47 and the radio unit 34. Inthis case, since the radiating directivity characteristic of thetransmitting antenna 33 of the satellite station is not always directedto the master station, in order to make the master station receive thecontrol frame without fail, it is necessary to transmit this controlframe utilizing a broad radiating directivity characteristic.

Such being the case, as explained in FIG. 10, the master station can bemade to receive the control frame without fail by transmitting thecontrol frame using only one patch element under the control of theantenna directivity characteristic control unit 42. However, it is notnecessarily required to use a patch element at the center 58 as shown inFIG. 10. Since with transmission using only one element, the radiatingelectric field intensity is weak, in order to make the master stationreceive the control frame without fail, the control frame is transmittedafter the feeding power to the patch element 58 is made greater than thefeeding power at the time of normal data frame communication, by thepower feeding power control unit 46.

In FIG. 17 the master station 81 receives the control frame transmittedfrom the satellite station using the receiving antenna 82, the masterstation 81 verifies by the frame distinguishing unit 88 via the radiounit 84 that the received frame is a control frame, and then the radiounit 84 starts to transmit only a carrier wave under the control of thedetermining function control unit 87. In this case, the master stationdoes not transfer the control frame to the backbone LAN.

Even if a data frame is transmitted from another satellite station whilethe master station is transmitting a carrier wave, the satellite stationdetermining an antenna directivity characteristic is not affected by it,since different transmitting frequencies are used for upwardtransmission, that is, from a satellite station to the master stationand downward communication, that is, from the master station to asatellite station, and both electric field intensities are constant.That is, in this case, the satellite station determining an antennadirectivity characteristic receives only carrier waves transmitted fromthe master station, and thereby no collision of a frame occurs. However,as described later, when the satellite station transmits a controlframe, when the control frame is transmitted via a backbone LAN, or whenanother satellite station transmits a control frame or a normal dataframe simultaneously, a collision occurs.

Therefore, it is necessary to clearly distinguish a control frametransmitted from a satellite station from a normal data frame. FIG. 22shows an example of a format for this control frame. As shown in thedrawing, for example, in the master station a control frame can beclearly distinguished from a normal data frame by making all bits forindicating the end point address and start point address of a frame “0”.Particularly, as shown in the drawing, in the master station a controlframe can be instantaneously distinguished by using a MAC (media accesscontrol) address part in the leading part of a frame. The start pointaddress field is a part for setting a unique address in each dataterminal. You can also make all start point addresses “1”. Or a controlframe can be distinguished from a normal data frame by using a partother than a MAC address part. That is, a format for a control frame canbe anything, only if it can be distinguished from a normal data frame.

Furthermore, as shown in FIG. 22, for example, in the case of theEthernet being a typical LAN, when a control frame collides with anormal data frame, by embedding a padding, that is, a bit string of 8bits with arbitrary contents in the data field of a control frame as aPAD, further embedding a frame check sequence data in the control frame,and making the length of the control frame the shortest possible in theEthernet, that is, 512 bits, it can be recognized that a collision hasoccurred in both a satellite station determining an antenna directivitycharacteristic and terminal which has transmitted data.

Thus, even if there is a satellite station determining a directivitycharacteristic, normal data communication can be prevented from beingaffected. On the other hand, the satellite station determining adirectivity characteristic stops determining, nullifies thedetermination, transmits a control frame again from the determiningfunction control unit 41, for example, after a random back-off time, anddetermines again.

Following the transmission of the control frame, the satellite stationdetects the receiving electric field intensity of a carrier wavetransmitted from the master station by the electric field intensitydetecting/storing unit 44, and starts to determine the direction of themaster station while changing the directivity characteristic of thereceiving antenna by changing the phase of power feeding power by aphase shifter as explained in FIGS. 3 and 4. In this case, the carrierwave, etc. received from the master station are not output from thereceiving control unit 43 to the LAN function unit 36. That is, sincethe level (amplitude) of the carrier wave is smaller the level(amplitude) of data, and since the receiving control unit 43 detectsdata using a threshold larger than the level of the carrier wave, thecarrier is never output to the LAN function unit 36.

In the determination of an antenna directivity characteristic, asexplained in FIG. 9, first, an angle θ which can receive a carrier wavein the strongest intensity from the master station in the overalldirection of a plane parallel to an antenna plane, is detected, and anangle φ is further detected by determining for 90 degrees of directionin a plane vertical to the antenna plane.

When an antenna directivity characteristic is determined, a determiningprocedure is executed again depending on the maximum value and theminimum value of detected electric field intensity, if necessary. First,the lowest limit of the electric field intensity of a carrier wavetransmitted from the master station is predetermined in the electricfield strength detecting/storing unit 44. Then, if an electric fieldintensity greater than the lowest limit is not detected whendetermining, a determining procedure is executed again and an optimaldirection of radiating beams is decided for the satellite station.

The lowest limit of receiving electric field intensity means a receivingelectric field intensity too weak to carry out normal communication.More specifically, for example, the value can be decided and set in thesystem by actually measuring such a limit in the stage of trialmanufacture for the commercialization of a wireless LAN system. Or sincethe value depends on the characteristics of a system, that is, thecharacteristics of components used and the transmitting power, the valuecan be calculated and set in the system. Or the value can also bedecided using the incidence of error frames.

The minimum value of the difference between the maximum value and theminimum value of the receiving electric field intensity of a carrierwave transmitted from the master station is stored in the electric fieldintensity detecting/storing unit 44 of the satellite station in advance,and when a carrier wave cannot be received in a state of having adifference greater than the minimum value, a determining procedure isexecuted again from the beginning, and an optimal direction ofdirectivity characteristic is decided for a satellite station antenna.

FIGS. 23A and 23B show a case where the success or failure of adetermination is judged by whether the minimum value of the differencebetween the maximum value and the minimum value of receiving electricfield intensity is greater or less than a predetermined value. FIG. 23Ashows a case where when a coordinate is changed on a plane parallel toan antenna plane as shown in FIG. 9, the measured difference between themaximum value and the minimum value of the receiving electric fieldintensity is greater than the predetermined value. In such a case thedetermination shall be regarded as a success. On the contrary, FIG. 23Bshows a case where the difference between the maximum value and theminimum value of the receiving electric field intensity is less than thepredetermined value and the determination is regarded as a failure.

Furthermore, when in the determination of the directivity characteristicof a satellite station antenna, the maximum value and the minimum valueof the receiving electric field intensity of a carrier wave from themaster station are detected, a ratio of the maximum value to the minimumvalue, that is, a ratio of “the maximum value/the minimum value” isstored in the electric field intensity detecting/storing unit 44. Then,if a ratio of the maximum measured value to the minimum measured valueis less than the ratio, a determination procedure can be executed againfrom the beginning and an optimal direction of radiating beams can bedecided for a satellite station antenna. Or, on the contrary, a ratio of“the minimum value/the maximum value” is stored in the electric fieldintensity detecting/storing unit 44 in advance. Then, if a ratio of theminimum measured value to the maximum measured value is the same as orgreater than the ratio, a determining procedure can be executed againfrom the beginning.

Next, the determination executed again after a determination isterminated and the optimal direction of directivity characteristic isfixed, and the normal transmission and reception of data, that is, thetransmission and reception of data frames between a satellite stationand the master station is started, is described below.

The satellite station stores in advance such a threshold receivingelectric field intensity of a data frame that normal communicationbetween the satellite station and the master station may be started tobe affected, in the electric field intensity detecting/storing unit 44,and detects the receiving electric field intensity of a normal dataframe received from the master station. When the receiving electricfield intensity of a data frame transmitted from the master stationbecomes less than a predetermined limit due to the movement of a dataterminal or a satellite station connected to the data terminal or theshift of the position of an antenna, an instruction to start todetermine is sent from the determining function, control unit 41 to thecontrol frame generating unit 45 as described above, a determination isre-started, and thereby an optimal communication environment can besecured again.

In this case, if an electric field intensity greater than the lowestlimit of receiving electric field intensity of a carrier wave from themaster station stored in advance as described above while determining isnot detected, a determining procedure can be executed once more. Thesame applies to the minimum value of the difference between the maximumvalue and the minimum value, a ratio of the maximum value to the minimumvalue and a ratio of the minimum value to the maximum value.

Furthermore, for the intensity of a receiving carrier wave from themaster station not only electric field intensity but also magnetic fieldintensity can be adopted as a standard. Furthermore, in an infrared raywireless LAN system, infrared ray intensity can also be adopted as astandard.

For another condition for determining again after the transmission andreception of a normal data frame is started between a satellite stationand the master station, there is an error of a data frame. As shown inFIG. 5, each of the satellite stations is provided with an FCS errorframe detecting unit/counter 48. If an error is detected in a framereceived from the master station, the number of the frames with an erroris counted, the determining function control unit 41 instructs to startto determine in the same way as described before, when the number offrames reaches the predetermined number of frames, and determines anantenna directivity characteristic in order to secure an optimalcommunication environment. In this case, the same processes as describedabove can be executed for the lowest limit, the minimum value of thedifference between the maximum value and the minimum value, a ratio ofthe maximum value to the minimum value and a ratio of the minimum valueto the maximum value of electric field intensity, and if therequirements are not met, a determination can be executed again.

It can be configured so that when the number of error framesconsecutively received reaches a predetermined number, a determinationis executed again in the same way as described above. Or it can also beconfigured that a timer 37 is started to operate when the first errorframe is received, and if the number of error frames received by thetime-out of the timer 37 reaches a predetermined number, a determinationof an antenna directivity characteristic is executed again. It can alsobe configured that if the predetermined number of error frames is notreceived during the time-out period of the timer 37, the counter iscleared after the time-out period elapses, and when an error frame isreceived again, the start of the timer 37 and the processes after thatare repeated.

Or it can also be configured that when an error frame is received, thetimer 37 is started to operate, and when the number of error framesreaches the predetermined number, a determination of an antennadirectivity characteristic is started. Even if the timer 37 is startedto operate and further several error frames are consecutively received,the counter and the timer are reset when a normal frame is receivedbefore the number of error frames reaches the predetermined number. Whenthe timer 37 time-outs, the counter is cleared.

It can also be configured that even when the timer 37 is started tooperate in this way, the same processes as described above are executedfor the lowest limit, the minimum value in difference between themaximum value and the minimum value, a ratio of the maximum value to theminimum value and a ratio of the minimum value to the maximum value ofreceiving electric field intensity, and a determination of an antennadirectivity characteristic is executed again.

Next, concerning the operation of the master station, it can also beconfigured that when a control frame is received from a satellitestation, and a carrier wave is returned to the satellite station, acarrier wave is transmitted in a state where transmitting power is madeless than the transmitting power at the time of transmission of a normaldata frame by the power feeding power control unit 89 shown in FIG. 17.Thus, the power consumption can be reduced.

When a data frame is transmitted from another satellite station or abackbone LAN while the master station is transmitting a carrier wavewith a transmitting power less than the transmitting power at the timeof a normal data communication and the satellite station is determiningan antenna directivity characteristic, it is anticipated that theelectric field intensity detecting/storing unit 44 of the satellitestation detects a discontinuous and rapid rise of electric fieldintensity. In this case, since an optimal direction of a normal antennadirectivity characteristic cannot be determined, an antenna directivitycharacteristic can be determined by the satellite station stopping thedetermining, clearing the result of the determination so far,transmitting a control frame again when the transmission of data framesis terminated or after a certain time determined by, for example, arandom back-off algorithm elapses, and making the master stationtransmit a carrier wave.

As described in detail above, according to the present invention, anoptimal communication environment can be secured without adjusting theposition of a data terminal, a satellite station or a satellite stationantenna, by adopting a satellite station antenna the radiatingdirectivity characteristic of which can be freely changed, transmittinga control frame from the satellite station, the master station startingto return a carrier wave, the satellite station determining such adirection of antenna directivity characteristic that a carrier wavetransmitted from the master station may be received with the maximumintensity, and fixing the directivity characteristic of a satellitestation antenna to the direction of the master station in a wireless LANsystem mainly using a millimeter wave.

Furthermore, the wireless LAN system can automatically cope with thedeterioration of a communication environment due to the movement of adata terminal or a satellite station, or the shift of the position of anantenna, and the best communication quality can be always provided bysetting conditions for the number of error frames allowed to be receivedin a satellite station, or the receiving electric field intensity of adata frame, and determining an optimal antenna directivitycharacteristic again when the conditions are not met.

The power in the master station can also be saved by making theintensity of a carrier wave transmitted from the master station whiledetermining, less than the intensity at the time of normal datacommunication.

Accordingly, according to the present invention a strong and flexiblewireless LAN system can be constructed, and the present inventiongreatly contributes to the realization of a high-speed wireless LANsystem using a millimeter wave in an unused wave range assigned to datacommunication.

1. A wireless local area network system comprising: a wireless localarea network master station for supporting communication betweensatellite stations belonging to a master station, and one or morewireless local area network satellite stations, wherein the satellitestation in the relevant local area network comprises an antenna fordynamically changing a directivity characteristic when receivingelectric waves from the master station; a control frame transmittingunit transmitting control frames prior to the commencement ofcommunication; and an antenna directivity characteristic controllingunit determining such a directivity characteristic that the receivingelectric field intensity of a carrier wave transmitted from the masterstation when receiving the relevant control frame may become a maximumby changing the directivity characteristic of said antenna, and themaster station in the relevant local area network system comprises acarrier wave transmitting unit starting to transmit carrier waves whenreceiving said control frame, and wherein directions of radiatingdirectivity characteristic can be freely changed on a hemisphericalplane of an antenna plane by changing each power feeding phase usingphase shifters.
 2. A wireless local area network system comprising: awireless local area network master station for supporting communicationbetween satellite stations belonging to a master station, and aplurality of wireless local area network satellite stations, wherein thesatellite station comprises: an antenna directivity characteristicadjusting unit adjusting the antenna directivity characteristic of areceiving antenna so that the receiving electric field intensity ofelectro-magnetic waves transmitted from the master station becomes amaximum, and the master station comprises electro-magnetic wavetransmitting unit transmitting electromagnetic waves with such intensityas to enable a satellite station to detect at least said receivingelectric field intensity while the directivity characteristic of therelevant receiving antenna is adjusted in the satellite station, andwherein directions of radiating directivity characteristic can be freelychanged on a hemispherical plane of an antenna plane by changing eachpower feeding phase using phase shifters.
 3. A transmitter-receiver forcommunicating with another party in a wireless local area network systemprovided with an antenna, the directivity characteristic of which can bedynamically changed when receiving electric waves, comprising: a controlframe distinguishing unit distinguishing a control frame transmittedfrom said communication partner from a data frame prior to thecommencement of communication; and a carrier wave transmitting unitstarting to transmit a carrier wave so that said communication partnermay determine such a directivity characteristic that the receivingelectric field intensity of said antenna may become a maximum, andwherein directions of radiating directivity characteristic can be freelychanged on a hemispherical plane of an antenna plane by changing eachpower feeding phase using phase shifters.
 4. The transmitter-receiveraccording to claim 3, wherein the antenna provided for saidcommunication partner is an active phased planar-array antenna.
 5. Thetransmitter-receiver according to claim 3, wherein said carrier wavetransmitting unit makes the transmitting power of the carrier waves lessthan the transmitting power at the time of a normal data frame whenreceiving said control frame.
 6. A method for optimizing communicationquality in a wireless local area network system comprising a masterstation for supporting communication between satellite stationsbelonging to the master station, comprising: enabling the relevantsatellite station to perform: transmitting a control frame to acommunication partner prior to the commencement of communication;determining such a directivity characteristic that the receivingelectric field intensity of a carrier wave transmitted from the masterstation in the relevant local area network may become a maximum whenreceiving said control frame by changing the directivity characteristicof an antenna, the directivity characteristic of which can bedynamically changed when receiving said control frame; and enabling themaster station in the relevant local area network system to perform thestep of starting to transmit a carrier wave when receiving said controlframe, and wherein directions of radiating directivity characteristiccan be freely changed on a hemispherical plane of an antenna plane bychanging each power feeding phase using phase shifters.
 7. A wirelesslocal area network system comprising: a wireless local area networkmaster station for supporting communication between satellite stationsbelonging to the master station, and one or more wireless local areanetwork satellite stations, wherein the satellite station in therelevant local area network comprises an antenna for dynamicallychanging a directivity characteristic when receiving electric waves fromthe master station; control frame transmitting means for transmittingcontrol frames prior to the commencement of communications; and antennadirectivity characteristic controlling means for determining such adirectivity characteristic that the receiving electric field intensityof a carrier wave transmitted from the master station when receiving therelevant control frame may become a maximum by changing the directivitycharacteristic of said antenna, and the master station in the relevantlocal area network system comprises carrier wave transmitting means forstarting to transmit carrier waves when receiving said control frame,and wherein directions of radiating directivity characteristic can befreely changed on a hemispherical plane of an antenna plane by changingeach power feeding phase using phase shifters.